The invention relates to a process and an apparatus including a power source connected to an electrode disposed in an evacuable coating chamber for reactively coating a substrate, for example with silicon dioxide (SiO.sub.2). This electrode is electrically connected to a target to be sputtered and the sputtered particles are deposited on the substrate with a process gas being supplied to the coating chamber.
In known processes for coating substrates by means of cathode sputtering and materials having a high affinity for the reactive gas, the problem arises that in addition to the substrate itself, other parts of the apparatus, like the inner wall of the process chamber or parts of diaphragms, are also coated with materials that have little or no electrical conductivity. This requires a frequent change of process parameters in the course of one single coating process or even a frequent interruption of the process as well as a frequent cleaning or replacing of parts of the apparatus.